Criticism of research methods used to set regulations affecting how much it costs to ship fresh produce by truck — at least in California — could delay their implementation.

The California Air Resources Board originally based its regulations on research that supported a correlation between the particulate matter emitted by diesel-burning engines, PM 2.5, and more than 20,000 early deaths per year in California. That assessment fell under scrutiny following revelations that Hien Tran, the agency’s lead author on the study, falsified his credentials, and that the board chairwoman Mary Nichols did not disclose that information to the rest of the board before the vote on the rule.

A new study the air resources board seems to be adopting suggests a smaller total — 9,000 people a year — die prematurely in California because of the effects of particulate matter.

That study found a causal relationship between engines burning diesel fuel and premature deaths but uses data from the EPA’s assessment of 116 U.S. cities. However, some say that data overestimate the emissions climate in California because of its proximity to the ocean and the eastward movement of pollution.

“We understand CARB has a public health mission, but the state of California has as much a stake in the wellbeing of the public and has a responsibility to protect the economy and jobs in the state as it does air quality, and that balance has not been present in that process,” said Dave Puglia, senior vice president of government affairs for Irvine, Calif.-based Western Growers.

In another twist, University of California-Los Angeles researcher James Enstrom is fighting for his job after claiming his research shows there is no link between PM 2.5 emissions and premature deaths. Enstrom said he believes his stance against the air resources board and its research is the reason behind his termination, according to media reports.

His appointment has been extended until March 31 while the grievance process is followed, said Phil Hampton, assistant director in the office of media relations for UCLA.

The produce industry is also taking a play out of the construction industry’s playbook. The construction industry’s heavy-duty trucks were the first to go through this process with the air resources board. It argued the original emissions estimates did not accurately reflect current emissions because of the economic downturn, which means less business, smaller fleets and less frequent use of trucks.

“It’s the same thing now in highway truck use,” Puglia said. “You go to the Port of Long Beach, and you can tell we’re in a state of reduced economic activity, so we’re going to compel CARB to reduce that number.”

The air resources board is expected to release proposed amendments to the regulation by the first week of November, after which it will hold a 45-day open comment period.